Methods and apparatus for imaging elongate objects

ABSTRACT

A storage phosphor cassette for use in recording radiographic images of elongated objects. The cassette comprises a shell and a single storage phosphor plate. The shell includes first and second opposite open ends. The single storage phosphor plate is housed within the shell and is adapted to be at least partially removable from the shell through the first and second open ends. A radiation image of the elongate object can be read by extracting a first portion of the single plate through one of the two opposing ends of the cassette and scanning the first portion of the single storage phosphor plate to obtain a first partial image, and then extracting a second portion of the single plate through the other of the two opposing ends of the cassette and scanning the second portion of the single storage phosphor plate to obtain a second partial image. The first and second partial images can be combined to form the image of the elongate object.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Ser. No. 11/250,225, entitled “METHODSAND APPARATUS FOR IMAGING ELONGATE OBJECTS” filed on Oct. 14, 2005 inthe name of Koren, and which issued as U.S. Pat. No. 7,304,321, whichitself claims priority from U.S. Ser. No. 60/619,261, entitled “METHODSAND APPARATUS FOR IMAGING ELONGATE OBJECTS”, filed on Oct. 15, 2004 inthe name of Koren, and which is assigned to the assignee of thisapplication.

FIELD OF THE INVENTION

The invention relates generally to the field of medical imaging, and inparticular to imaging elongated objects. More specifically, theinvention relates to imaging elongated body regions, such as the fullspine or the leg. A particular use for such imaging is in computedradiography (CR).

BACKGROUND OF THE INVENTION

X-ray imaging technology provides a non-invasive technique forvisualizing the internal structure of an object of interest by exposingthe object to high energy electromagnetic radiation (i.e., X-rays).X-rays emitted from a radiation source pass through the object and areabsorbed at varying levels by the internal structures of the object. Asa result, X-ray radiation exiting the object is attenuated according tothe various absorption characteristics of the materials which the X-raysencounter.

The absorption characteristics of the object of interest may be capturedby placing the object between a high energy electromagnetic radiationsource and an image recording medium. As radiation from the sourcepasses through the object, the radiation impinges on the image recordingmedium with an intensity related to the attenuation caused by thedifferent absorption characteristics of the object. The impingingradiation causes a change in the image recording medium that isproportional to the radiation intensity, thereby storing informationabout the internal structure of the object. The image recording mediummay then be processed to recover the stored information by, forinstance, converting it into digital form. Common types of imagerecording media include sheet film, phosphor media, and the like.

Phosphor plate technology has emerged as a valuable image recordingmedia for computed radiography (CR). When electromagnetic radiation,such as X-ray radiation, impinges on a phosphor plate, the radiationinteracts with the phosphor lattice of the plate. The phosphors in theplate store energy proportional to the intensity of the impingingradiation. This energy can later be released by scanning the plate witha laser to excite the phosphors in the plate (i.e., by causing thephosphors to fluoresce). The excited phosphors release radiation thatcan be detected, quantified and stored as values representing pixels inan image.

Some imaging procedures require exposure to radiation of relativelylarge-dimensioned objects, referred to generally as elongate objects.Elongate objects typically have at least one dimension larger thanstandard large-sized commercially available phosphor plates. Forexample, in various medical imaging procedures, elongate structuresinvolved in full-leg or spine examinations may need relatively longportions of the body to be imaged at once. Such procedures are oftenreferred to as “long bone” imaging and typically require specializedequipment to accommodate the elongate properties of the anatomy beingimaged. In addition, imaging of elongate objects in the industrialsetting is often desirable. For example, non-destructive imaging to testfor structural integrity of structural supports such as pillars orload-bearing walls and/or imaging of plumbing such as pipes may includeelongate objects that extend further than the capacity of a singleconventional phosphor plate.

Conventional size radiographic image acquisition units are limited insize and unsuitable for imaging elongated body regions such as the fullspine or the leg. When it is necessary to obtain a radiographic image ofa full spine or leg, several approaches have been used. If film/screentechnology is used, either an extra long, non-standard radiographic filmis used. For example, see U.S. Pat. No. 5,130,541 (Kawai).Alternatively, as disclosed in U.S. Pat. No. 3,774,045 (Trott) and U.S.Pat. No. 3,725,703 (Bucky), a cassette or cart is provided for holding aplurality of overlapping conventional sized film cassettes or packs.

A further alternative involves placing two or more standard sized CRphosphor plates (e.g., 35×43 cm phosphor plates) lengthwise adjacent toone another in a specialized cassette. The combined lengths of themultiple plates may be sufficient to image an elongate object having adimension greater than the longest dimension of any single phosphorplate. The term “cassette” refers generally to any of various casings,cartridges or containers adapted to hold other material, and moreparticularly, adapted to hold one or more image recording media (e.g.,one or more phosphor plates) to protect against damage from directhandling, contact or exposure. For example, a cassette may be formed asa rigid encasement providing a shell that can withstand the weight of apatient, rough handling, accidental falls, etc. A cassette typicallyincludes some form of opening that permits insertion and extraction ofthe image recording media into and out of the cassette.

Cassettes employing two or more storage phosphor plates/screens havebeen disclosed. For example, see commonly assigned U.S. Pat. No.6,852,987 (Steklenski), U.S. Pat. No. 6,696,691 (Foos), and U.S. Pat.No. 6,744,062 (Brahm). See also U.S. Pat. No. 6,843,598 (Minnigh), U.S.Pat. No. 6,273,606 (Dewaele), EP 1 312 977 (Delaby), JP 2000-241920(Sasada), JP 2002-202571 (Nakajo), JP 2000-267210 (Sasada), JP2000-250153 (Sasada), and JP 2000-258861 (Sasada).

FIG. 1 illustrates an exemplary elongate body imaging apparatus. Theapparatus includes a cassette 100 having a width X and a length Y.Cassette 100 is adapted to hold a pair of phosphor plates 150 a and 150b, each having a width x and a length y. In general, the length Y ischosen to accommodate a desired long bone imaging procedure, forexample, an examination of an entire leg or spinal column. The lengthyis typically equal to the length of conventional phosphor platesproduced by major vendors of imaging plates, and is insufficient, on itsown, to capture complete image information for the entire elongateobject.

Phosphor plates 150 a and 150 b are placed in cassette 100 in anoverlapping relationship to form an overlap region 155 having a width u.Together, the dimensions of plates 150 a and 150 b (i.e., 2y-u) issufficient to capture image information of the entire elongate object.

Cassette 100 may include reference or fiducial marks (not shown) thatcast a “shadow” on portions of the plates, for example, in overlapregion 155. The reference marks may be any generally X-ray resistantmaterial arranged in a known pattern or relationship to one anotherthat, when exposed to X-ray radiation, will cast a distinguishableshadow on the phosphor plates. For example, the reference marks may be aplurality of parallel and perpendicular lines that, when exposed,imprint a grid pattern on the phosphor plates. The reference marksprovide fiducial information that may be referenced to correct foralignment errors and as a guide to facilitate image stitching, asdiscussed in further detail below.

The above described action of overlapping multiple plates in a cassettemay be repeated to achieve coverage of elongate objects of any desireddimension. For example, a cassette may be adapted to hold a third platehaving an overlapping relationship with the bottom edge of plate 150 b.Any number of plates may be positioned together to arrive at a lengthsufficient to obtain image information from a desired elongate object.

After the cassette is exposed to radiation in the presence of theelongate object, phosphor plates 150 a and 150 b are removed from thecassette and are loaded individually and successively into a CR imagereader adapted to acquire image information stored on the standard sizedplates. Accordingly, the CR image reader obtains a first partial imagefrom phosphor plate 150 a and a second partial image from phosphor plate150 b.

However, the separate partial images make diagnostic and/or examinationof the elongate object relatively difficult. Thus, the CR image readermay include image processing techniques adapted to stitch the partialimages together using alignment information provided by the referencemarks imprinted on the partial images to form a single image of theelongate object. Some stitching methods have been disclosed, forexample, see commonly assigned U.S. Pat. No. 6,895,106 (Wang).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cassette which can beemployed to image elongated objects in a single exposure.

Another object of the present invention is to provide such a storagephosphor cassette.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

According to one aspect of the present invention, there is provided astorage phosphor cassette for use in recording radiographic images ofelongated objects. The cassette comprises a shell and a single storagephosphor plate. The shell includes first and second opposite open ends.The single storage phosphor plate is housed within the shell and isadapted to be at least partially removable from the shell through thefirst and second open ends.

According to another aspect of the present invention, there is provideda method of forming a composite digital image of an elongate object froma radiation image formed on a single extended length storage phosphorplate disposed within a cassette. The method includes the steps of:extracting a first portion of the single plate through a first end ofthe cassette; scanning the first portion to obtain a first partialimage; extracting a second portion of the single plate through a secondend of the cassette opposing the first end; scanning the second portionto obtain a second partial image; and combining the first and secondpartial images to form the image of the elongate object.

According to a further aspect of the present invention, there isprovided a method of reconstructing a radiation image of an elongatedobject. The method comprising the steps of: extracting a first portionof a single storage phosphor plate of length L disposed within acassette through a first end of the cassette, the first portion having alength S1 wherein S1<L; scanning the first portion to read storageinformation on the first portion to obtain a first partial image;erasing the stored information on a first segment of the first portion,the first segment having a length E1 wherein E1<S1; extracting a secondportion of the single storage phosphor plate through a second end of thecassette, the second end opposing the first end, the second portionhaving a length S2 wherein S2<L and S1+S2>L; scanning the second portionto read storage information on the second portion to obtain a secondpartial image; and erasing the remaining stored information stored onthe storage phosphor plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1 shows a diagrammatic view of an exemplary elongate body imagingcassette comprising a pair of storage phosphor plates.

FIG. 2 shows a diagrammatic view of a radiographic imaging cassettehaving an extended length plate, in accordance with the presentinvention.

FIGS. 3A-3D illustrate diagrammatic views of a conventional scanningprocess for obtaining a long bone image from a pair of standardizedmedical imaging plates.

FIGS. 4A and 4B illustrate diagrammatic views of an exemplary scan anderase cycle of an extended length phosphor plate, in accordance with oneembodiment of the present invention.

FIGS. 5A-5F illustrate diagrammatic views of a scan and erase processfor an extended length plate, in accordance with one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the preferred embodiments ofthe invention, reference being made to the drawings in which the samereference numerals identify the same elements of structure in each ofthe several figures.

As discussed above, conventional imaging of elongate objects involvesstitching together two or more partial images obtained from separate andrespective phosphor plates. However, employing multiple phosphor platescomplicates the imaging process. First, the cassette typically includesmechanisms to ensure that the plates are substantially aligned, both inrotation with respect to one another and in preserving a desired overlapregion. Moreover, because the complete latent image is stored onseparate phosphor plates, the act of scanning the individual platesintroduces further alignment difficulties that typically requirerelatively sophisticated imaging algorithms to remedy before the partialimages may be stitched together to form a viewable and faithful image ofan elongate object.

A stitching algorithm may need to identify and compensate for bothrotational and angular misalignment between the partial images and arange of translational misalignment in the overlap region. Moreover,images that are successfully stitched together may include, to someextent, distortion caused by the image processing employed to correctfor the various alignment errors. Conventional stitching algorithmsoften rely on the redundant information provided in the overlapregion(s) of the multiple phosphor plates. For example, since portionsof plates 150 a and 150 b in overlap region 155 are exposed toattenuated radiation from the same parts of the object being imaged,both plates should record, to some extent, the same information in thisoverlap region. However, the absorption characteristics of the upperphosphor plate results in relatively faint exposure on the lower plate.This reduction in the “signal” on the lower plate reduces thecorrelative properties of this supposed redundant information and makesstitching relatively difficult, reducing the precision of the alignmentalgorithms.

Applicant has appreciated that some of the problems associated withscanning elongate objects by employing multiple standardized phosphorplates may be alleviated or reduced by using a single extended lengthphosphor plate. FIG. 2 illustrates an imaging apparatus for scanningelongate objects, in accordance with one embodiment of the presentinvention. The imaging apparatus includes a cassette 200 dimensioned toa length capable of accommodating long bone imaging, such as a full-legor full-spine examination. In particular, cassette 200 is provided witha length Y equal to or greater than the elongate object to be imaged.Cassette 200 is adapted to hold a single phosphor plate 250 having alength Y′ sufficient to capture image information of the elongateobject.

As will become more apparent with the description below, cassette 200includes an elongate rectangular shell having two opposing ends. Plate250 is disposed within cassette 200 such that it can be moved relativeto the shell (for example, by a sliding motion) so as to be at leastpartially removed from either end of the cassette. As such, plate 250can be accessed from cassette 200 through either end of the cassette byextraction of the plate from either cassette end. Accordingly, cassette200 is a double-ended cassette comprising a single plate. When plate 250is disposed within the shell, the cassette is preferably substantiallylight-tight.

It should be appreciated that the extended length plate may bemanufactured to correspond to lengths conventionally achieved using anynumber and combination of multiple plates. For example, an extendedlength plate may include dimensions achieving the same coverage as two,three, four or any number of multiple plates of any combination ofdimensions positioned together, as the aspects of the invention are notlimited in this respect.

The introduction of a single extended length plate obviates the need tocarefully arrange multiple plates in the cassette to avoid alignmenterrors. In particular, since no overlap region is required, the cassetteneed not include structure adapted to properly place and hold multiplecassettes in an overlapping relationship. In addition, because the plateis integral, errors caused by rotational misalignment during exposureare eliminated. As discussed in further detail below, single plateimaging includes further benefits during the scanning process.

In conventional long bone imaging, after multiple phosphor plates havebeen exposed to X-ray radiation, a first plate is extracted from thecassette and loaded into a CR image reader. An example of a CR imagereader is described in U.S. Pat. No. 6,791,101 ('101) to inventor Koren,which is incorporated herein in its entirety. The CR image reader may beadapted to perform a complete scan of some predetermined maximum length,referred to as the scan length. For example, the CR image reader may bedesigned with a scan length of approximately 43 cm to accommodate andprocess standard sized phosphor plates in a single scanning procedure.The term “scan length” with reference to a CR image reader, defines themaximum length of an image recording medium that the CR image reader iscapable of capturing in a single scan. In general, the scan-length isclosely related to the size of the CR image reader. For example, when aphosphor plate is loaded into the CR image reader, the dimensions of theimage reader can only accommodate some maximum length of plate. Many CRimage readers are designed to accommodate the standard large-sizedphosphor plate available on the market (e.g., a 35×45 cm phosphorplate). Such a scan-length is insufficient to acquire a long bone imagein a single scanning operation.

FIGS. 3A-3D illustrate snapshots of a conventional scanning process forobtaining a long bone image from a pair of standardized medical imagingplates.

FIG. 3A illustrates a cassette 300 inserted into a CR image reader 360.The cassette holds a pair of standard sized plates 350 a and 350 b thathave been exposed to radiation. First, plate 350 a is extracted fromcassette 300 by pinch rollers 366 a and 366 b and guided intocylindrical segment 362, for example, a cylindrical drum providingconformal support for the phosphor plate as it enters CR image reader360. CR image reader also includes scanning components 365 adapted tostimulate the phosphor plate (e.g., via a laser beam) and detectstimulated radiation emitted by the phosphor plate in response to thelaser beam (e.g., via a photo multiplier tube (PMT)), such as describedin the '101 patent. CR image reader 360 also includes erasing lamps 364adapted to erase information from the phosphor plates as described infurther detail below.

In FIG. 3B, phosphor plate 350 a has been fully inserted into the imagereader and is ready for scanning by scanning components 365. Scanningcomponents 365 may include a laser source capable of providingstimulating radiation to the surface of the cylindrical segment 362 anda detector capable of detecting radiation emitted by phosphor plate 350a in response to laser energy impinging on its surface. It should beappreciated that the scan length of CR image reader 360 depends, inpart, on the circumference of cylindrical segment 362 and/or onmechanical limitations of scanning components 365. After phosphor plate350 a has been scanned and a first partial image obtained, rollers 366 aand 366 b reverse direction to guide phosphor plate 350 a back intocassette 300 as illustrated in FIG. 3C, until the plate is securely backin the cassette as shown in FIG. 3D.

To reduce the overall processing time of acquiring images from phosphorplates and returning the plate(s) to the cassette for re-use, thephosphor plates are often erased simultaneously with insertion back intothe cassette. Erasing a phosphor plate may involve exposing the plate tobright light so that the phosphors in the plate release any energyremaining in the phosphor lattice plate after a scanning cycle has beencompleted.

As shown in FIG. 3C, erasing lamps 364 are disposed between the pinchrollers. When the rollers are activated in a direction to guide thephosphor plate into the cassette, erasing lamps 364 are turned on toexpose the plate to light as it passes underneath. As a result, plate350 a discharges its remaining stored energy before being inserted intothe cassette for a subsequent exposure. The second phosphor plate 350 bmay then be loaded into the CR image reader and the process repeated toobtain a second partial image. After both partial images have beenobtained, image processing algorithms may process the partial images to,for example, locate the reference marks, determine the extent ofmisalignment between the images, compensate for the misalignment, andstitch the two partial images together to form a single image of theelongate object.

Applicant has developed methods and apparatus for scanning and erasing asingle extended length phosphor plate (such as shown in FIG. 2) in a CRimage reader designed to operate with a scan length less than the lengthof the extended length phosphor plate. For example, in one embodiment,methods and apparatus for scanning and erasing an extended lengthphosphor plate in a CR image reader designed for standard large-sizedplates are provided to facilitate scanning of elongate objects such asthose encountered in various long bone examination procedures.

FIGS. 4A and 4B illustrate snapshots during an exemplary scan and erasecycle of an extended length phosphor plate, in accordance with oneembodiment of the present invention.

FIG. 4A illustrates a cassette 400 for handling an extended lengthphosphor plate 450, inserted into CR image reader 460. CR image reader460 may be structurally similar or substantially the same as CR imagereader 360 illustrated in FIGS. 3A-3D. In particular, CR image reader460 may have the same scan length as CR image reader 360.

FIG. 4B illustrates phosphor plate 450 fully inserted into CR imagereader 460, such that it is in position for scanning by opticalcomponents 465. CR image reader than performs a scan of a portion ofphosphor plate 450 by means of optical components 465 to obtain a firstpartial image of the elongate object. Rollers 466 a and 466 b may thenreverse direction to guide phosphor plate back into cassette 400.Cassette 400 is then unloaded from the CR image reader and the otherside is inserted into the CR image reader and the process is repeated toobtain a second partial image.

As discussed above, stitching of partial images from distinct imagingplates, as is done conventionally, often relies on redundant informationavailable in an overlap region of the plates. According to aspects ofthe present invention, this redundant information may be obtained byscanning an over-scan region of the single extended phosphor platemultiple times. For example, a region of the plate 450 near the centermay be scanned once during a first scan and again during a second scan.However, Applicant has appreciated that conventional erasing procedures(e.g., scan and erase cycles as described in connection with FIGS.3A-3D) may erase information in the over-scan region before the secondscan takes place, resulting in the loss of the information used, atleast in part, to align and stitch the two partial images together.

Applicant has developed an erase timing schedule for extended lengthplates (such as shown in FIG. 2) that preserves information in theover-scan region without requiring additional erasing steps. This erasetiming schedule is more particularly described with reference to FIGS.5A-5F.

FIGS. 5A-5F illustrate a scan and erase process for an extended lengthplate in accordance with one embodiment of the present invention. Forexample, phosphor plate 550 may be scanned and erased by CR image reader460 illustrated in FIGS. 4A and 4B.

FIG. 5A illustrates an extended phosphor plate 550 having a length L,for example, equal to or greater than a length of an elongate object tobe imaged. Length S corresponds to the scan length of a CR image reader.Since the scan length of CR image reader 460 may be designed toaccommodate and process standard sized plates in a single scan, length Smay be significantly less than length L. For the combination of plate550 and CR image reader 460, the scan length S is about half the lengthL plus an additional length o that contributes to the over-scan region,as discussed in farther detail below.

Due to the width of the pinch rollers in a CR image reader (or otherplate transport mechanisms) and due to the placement of the erasinglamps, CR image reader 460 is capable of erasing a larger portion of theplate in a scan and erase cycle than it is capable of scanning. Forexample, CR image reader includes a scan area that runs fromapproximately an end of cylindrical segment 462 (labeled as 462 b inFIG. 4B) to approximately a beginning of cylindrical segment 462(labeled as 462 a in FIG. 4B). CR image reader also includes an erasearea situated between the rollers, extending approximately between 464 aand 464 b (shown in FIG. 4B). When using an extended length plate (seeFIG. 4B), there is a portion of the plate between the beginning of thescan area 462 a and the end of the erase area 464 b that is in aposition to be erased if the lamps are turned on before orsimultaneously with the reverse activation of the rollers. Because thisportion of the plate is outside the scan area, it may be erased but notscanned during a first scan and erase cycle. Thus, the erase length E(shown in FIG. 5A) is longer than scan length S.

FIG. 5B illustrates plate 550 after it has been exposed to X-rayradiation, such that it stores a latent image of, for example, a longbone of a patient. Plate 550 may then be loaded into the CR imagereader, with end 550 a inserted first, and scanned to obtain a firstpartial image. As indicated by shading in FIG. 5C, portion 552 ofphosphor plate 550 has been scanned and a portion of its stored energyreleased and detected to form the first partial image. Portion 554 ofplate 550 has not been scanned and thus retains all of its exposureenergy. It should be appreciated that scanned portion 552 includes anarea over half the length of phosphor plate 550, allowing for anover-scan region to be scanned on both the first and second scan cycles.

To avoid erasing information in the over-scan region, the rollers may beactivated to guide the plate out of the scan area in a reverse directionfor a predetermined interval of time before the erasing lamps are turnedon. The interval of time between the instant the plate begins moving ina direction towards the cassette and the instant the erasing lamps areactivated is referred to as the “wait interval.” The wait intervalpreserves the information in at least the over-scan region as it passesthrough the erase zone and into the cassette. Once the wait interval hasexpired, the erasing lamps are activated and the remainder of portion552 is erased.

FIG. 5D illustrates phosphor plate 550 after the first scan and erasecycle. The wait interval includes the time necessary for portion 565 ofphosphor plate 550 to pass through the erase zone of the CR imagereader, including portion 552 a of scanned portion 552. After the waitinterval, the erasing lamps are activated to erase the remaininginformation in portion 552 b. Although the exemplary wait interval inthe embodiment shown in FIGS. 5A-5F was chosen to erase substantiallyhalf of portion 552, aspects of the invention are not limited in thisrespect. Any wait interval may be chosen that preserves information in adesired portion of the phosphor plate.

After the first scan and erase cycle, phosphor plate 550 may then beloaded into the CR image reader with side 550 b inserted first to obtaina second partial image. That is, the end of the phosphor plate includingportion 554 may be loaded into the CR image reader. As before, pinchrollers (or some other transport mechanism) guides the phosphor plateinto the image reader and a second scan is performed.

FIG. 5E illustrates phosphor plate 550 after a second scan cycle toobtain a second partial image. As with the first scan, more than half ofthe phosphor plate undergoes scanning from the optical scanningcomponents of the CR image reader. Accordingly, all of portion 554 isscanned and an over-scan region 552 baof preserved scanned portion 552 aundergoes a second scan cycle. The second scan cycle releases some ofthe energy in over-scan portion 552 a left-over from the first scan toprovide redundant information, as discussed in further detail below.

After the second scan cycle, the pinch rollers are activated in thereverse direction and the erasing lamps are turned on before orsubstantially at the same time as the rollers to erase the remaininglength of the plate. Since the un-erased portions 554, 552 ba and 552 bare contiguous and of a length less than length E, a full erase cycle iscapable of removing all the remaining latent energy stored in thephosphor plate.

FIG. 5F illustrates phosphor plate 550 after the second scan and erasecycle, wherein the entire plate has been erased and is ready for asubsequent exposure to X-ray radiation.

It should be appreciated that the various portions illustrated in FIGS.5A-5B are merely exemplary. Portion lengths and relationships to oneanother may vary depending on factors that may include any one orcombination of the size and configuration of the CR image reader (e.g.,the length of the erase zone, maximum scan length, maximum erase length,etc.), the length of the phosphor plate, a desired over-scan region,etc., and aspects of the invention are not limited for use with therelative dimensions illustrated in the embodiments described herein.

In general, when an exposed phosphor plate undergoes scanning, forexample, by directing a laser beam to impinge on the surface of thephosphor plate, not all of the energy stored in the phosphor lattice isreleased. For example, scanned portion 552 b retains an attenuated formof the image information stored during exposure. Accordingly, whenover-scan region 552 ba undergoes a second scan cycle, CR image readerwill obtain an attenuated copy of the image information obtained fromthis region during the first scan cycle. The image information in theover-scan region obtained during the first and second scan cycle maythen be matched up in order to align and stitch the partial imagestogether.

As discussed above, in conventional long bone imaging, the “redundant”information is obtained by overlapping the two phosphor plates in thecassette. However, due to the absorption characteristics of phosphorplates, relatively little information is available on the phosphor platesituated underneath in the overlap region. Accordingly, conventionalstitching techniques may rely on reference marks and may need to employreference patterns outside of the overlap region, resulting in furtherobstruction to the content of interest (i.e., the medical imagecontent). Moreover, in imaging procedures where the extended lengthplate achieves the same coverage as a conventional procedure using morethan two conventional plates, still only a single over-scan region maybe necessary. Accordingly, multiple overlap regions and stitchingoperations required in combining partial images from more than twoconventionally dimensioned plates may be avoided.

In some embodiments, the redundant information in the over-scan regionis sufficient to align and stitch the partial images into a single imagewithout the aid of reference marks. That is, the information in the twocopies of the over-scan region (i.e., the initial and attenuated copies)may be matched and aligned without having to rely on externally producedreference marks.

For example, in the first partial image acquired during the first scan,the ending edge is recorded by the last image pixel line. Subsequently,in the second partial image acquired during the second scan, the endingedge of the first partial image is recorded in the second partial image.Accordingly, the ending edge of the first partial image can be detectedwithin/from the second partial image. If it is desired to stitch thesecond partial image to the first partial image, it may be necessary torotate/position the second partial image so that it can be stitchedalong the ending edge of the first partial image.

Detection of the ending edge of the first partial image within thesecond partial image can be accomplished by detecting the signaldiscontinuity. That is, since the signal in the over-lap region is readin the first scan, its pixel intensity is reduced. This ending edgedetermines the relative position and rotation of the second partialimage relative to the first partial image.

It is possible that the second partial image may need to be rotatedbased on the detected ending edge of the first partial image from thesecond partial image.

Further, the second partial image may need to be rotated by 180 degrees(prior to stitching it to the first image) so as to properly match thetwo images. This is due to the single imaging plate. That is, if eachend of the single imaging plate is inserted into the CR reader, then onepartial image needs to be rotated by 180 degrees to properly match thetwo partial images.

With regard to stitching the two partial images, commonly assigned U.S.Pat. No. 6,895,106 (Wang) discloses the use of information in theoverlap region and/or scan ending edges for image stitching. It is notedthat the stitching can be accomplished manually or automatically.

The present invention provides for the use of simpler cassettes that donot require built in patterns or marks to imprint the partial images, oralternatively, may permit the use of simpler reference marks and/orreference marks limited in location to the over scan region. Inaddition, in the absence of reference marks (or in the presence ofrelatively simple reference marks) more of the content of interest inthe image is free from super positional interference of referenceinformation that is not clinically useful and detracts from the medicalexamination and/or diagnosis.

It should be appreciated that while aspects of the invention mayfacilitate the use of simpler reference marks or their eliminationaltogether, any type of reference marks or fiducial technique may beused and is not limited in this respect. For example, it may bedesirable to employ the same reference marks and alignment algorithmsdeveloped for multi-plate procedures in extended plate procedures toreduce further development costs.

As discussed above, in conventional elongate object scanning operations,misalignment between partial images obtained from the separate imagingplates may be caused, in part, by rotation of the plates with respect tothe direction in which the plate is guided into the image reader. Forexample, as the pinch rollers in FIGS. 3A-3D guide the individualstandard-sized plates into the CR image reader, the plates may tend todeviate from the intended path by differing amounts. Large deviationsmake stitching more difficult and result in relatively significantdistortion in the image due to image processing techniques employed tocorrect the alignment errors. The extended length of the phosphor platesof the present invention helps to stabilize the plate as it is guidedinto the CR image reader to reduce the amount of possible rotation. Inparticular, since a portion of the extended phosphor plate remains inthe cassette as the plate is guided into the CR image reader, and duringscanning (see FIG. 4B) the cassette constrains the plate and limits itsrotation and deviation from its intended scanning position. Thereduction in alignment errors results in simpler stitching and lessdistortion in the resulting images.

It should be appreciated that various aspects of the invention may beused in connection with imaging not only of elongate objects in medicalor industrial settings, but may be used in any circumstance whereinconventionally dimensioned phosphor plates are insufficient to providecoverage for an elongate object of which image information is sought.

The above-described embodiments of the present invention can beimplemented in any of numerous ways. For example, the embodiments may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers. It should beappreciated that any component or collection of components that performthe functions described above can be generically considered as one ormore controllers that control the above-discussed function. The one ormore controller can be implemented in numerous ways, such as withdedicated hardware, or with general purpose hardware (e.g., one or moreprocessor) that is programmed using microcode or software to perform thefunctions recited above.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. In particular, single extendedphosphor plates may used in connection with a variety of differentcassettes and CR image readers and are not limited to the exemplaryequipment illustrated herein. In addition, scan and erase cycles may betimed according to size and configuration constraints or any CR imagereader. Accordingly, the foregoing description and drawings are by wayof example only.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing”, “involving”, andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The presently disclosed embodiments are thereforeconsidered in all respects to be illustrative and not restrictive. Thescope of the invention is indicated by the appended claims, and allchanges that come within the meaning and range of equivalents thereofare intended to be embraced therein.

1. A storage phosphor cassette for use in recording radiographic imagesof elongated objects, comprising: a shell having first and secondopposite open ends; and a single storage phosphor plate housed withinthe shell and adapted to be at least partially removable from the shellthrough the first and second open ends, wherein the shell has nointernal structure preventing free sliding movement of the plate in theshell for partial removal from either of the first and second open ends.2. The storage phosphor cassette of claim 1, further comprising meansfor partially removing the single plate from the shell through the firstand second open ends.
 3. The storage phosphor cassette of claim 1,further comprising means for slidably moving the single plate relativeto the shell whereby the single plate protrudes through either the firstor second open end.
 4. The storage phosphor cassette of claim 1, whereinthe single plate is either flexible or substantially rigid.
 5. Animaging system, comprising: an imaging cassette adapted to be exposed toradiation of an elongate object, the cassette having a single storagephosphor plate and two opposing ends through which at least a portion ofthe single plate can be extracted; wherein the cassette has no internalstructure preventing free sliding movement of the plate in the cassettefor partial removal from either of the two opposing ends; a storagephosphor reader adapted to (1) extract a first portion of the singleplate through one of the two opposing ends of the cassette and scan thefirst portion of the single storage phosphor plate to obtain a firstpartial image, and (2) extract a second portion of the single platethrough the other of the two opposing ends of the cassette and scan thesecond portion of the single storage phosphor plate to obtain a secondpartial image; and means for combining the first and second partialimages to form the image of the elongate object.
 6. A method of readinga radiation image of an elongate object, comprising the steps of:providing a cassette exposed to radiation, the cassette having a singlestorage phosphor plate and two opposing ends through which at least aportion of the single plate can be extracted; wherein the cassette hasno internal structure preventing free sliding movement of the plate inthe cassette for partial removal from either of the ends of thecassette; extracting a first portion of the single plate through one ofthe two opposing ends of the cassette and scanning the first portion ofthe single storage phosphor plate to obtain a first partial image;extracting a second portion of the single plate through the other of thetwo opposing ends of the cassette and scanning the second portion of thesingle storage phosphor plate to obtain a second partial image; andcombining the first and second partial images so as to form the image ofthe elongate object.
 7. The method of claim 6, further comprising thesteps of: identifying, in the first partial image, an ending edge of thescanned image recorded by a last image pixel line, the ending edgeidentified in the first partial image being defined as a firstreference; detecting, in the second partial image, the ending edge ofthe first scanned image, the ending edge detected in the second partialimage being defined as a second reference; and combining the first andsecond partial images by aligning the first and second references. 8.The method of claim 7, wherein the step of combining is accomplished byrotating the second partial image to align the first and secondreferences.
 9. The method of claim 7, wherein the step of detecting theending edge in the second partial image is accomplished by detectingsignal discontinuity caused by scanning the first portion of the plate.10. A method of forming a composite digital image of an elongate objectfrom a radiation image formed on a single extended length storagephosphor plate disposed within a cassette, wherein the cassette has nointernal structure preventing free sliding movement of the plate in thecassette for partial removal from either of first and second ends of thecassette, comprising the steps of: extracting a first portion of thesingle plate through a first end of the cassette; scanning the firstportion to obtain a first partial image; extracting a second portion ofthe single plate through a second end of the cassette opposing the firstend; scanning the second portion to obtain a second partial image; andcombining the first and second partial images to form the image of theelongate object.
 11. The method of claim 10, further comprising thesteps of: identifying, in the first partial image, an ending edgerecorded by a last image pixel line, the ending edge identified in thefirst partial image being a first marker; detecting, in the secondpartial image, the ending edge, the ending edge detected in the secondpartial image being a second marker; and combining the first and secondpartial images by aligning the first and second markers.
 12. The methodof claim 11, wherein the step of combining is accomplished by rotatingthe second partial image relative to the first partial image to alignthe first and second markers.
 13. The method of claim 11, wherein thestep of detecting the ending edge in the second partial image isaccomplished by detecting signal discontinuity.
 14. A method of forminga composite digital image of an elongate object from a radiation imageformed on a single extended length storage phosphor plate disposedwithin a cassette, wherein the cassette has no internal structurepreventing free sliding movement of the plate in the cassette forpartial removal from either of first and second ends of the cassette,comprising the steps of: positioning a first end of the cassetterelative to a storage phosphor reader; extracting a first portion of thesingle plate through the first end of the cassette; scanning the firstportion to obtain a first partial image; after scanning the firstportion, repositioning the cassette such that a second end of thecassette, opposite the first end, is positioned relative to the storagephosphor reader; extracting a second portion of the single plate throughthe second end of the cassette; scanning the second portion to obtain asecond partial image; and combining the first and second partial imagesto form the image of the elongate object.